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E C 0 R 7-Eleven Store#19976 Quarterly Groundwater Monitoring and Remediation Progress Report(2Q2003) September 11, 2003 Page 4 maximum concentrations of 0 0087 mg/kg and 9 3 mg/kg, respectively MtBE and TBA were reported at maximum concentrations of 33 mg/kg (T1 N@13') and 18 mg/kg (T3N@13'), respectively Between June 23 and July 7, 2003, Glacier Environmental installed two new double-walled fiberglass USTs one 10,000-gallon premium unleaded gasoline UST, and one 15,000-gallon regular unleaded gasoline UST, and associated piping and dispensers (Figure 2) In order to accommodate the new 15,000-gallon UST, Glacier excavated approximately 288 cubic yards of soil, expanding the UST pit to the west MONITORING AND SAMPLING PROCEDURES The depth to water was measured in monitoring wells MW-1 through MW-7, MWAA, MW-4A, and MW-5A from top of casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were also collected from each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor Well purging and sampling equipment is thoroughly cleaned prior to purging and sampling each well The sampling procedure for each well includes measuring the water level and checking for the presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear Teflone bailer or an oil-water interface probe Wells not containing LPH are purged of approximately three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment and purging methods used for the current sampling event are noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity are monitored in order to document that these parameters are stable prior to collecting samples After purging, water levels are allowed to recover to 80% of the original levels prior to collection of the water sample Groundwater samples are collected using a disposable Teflone bailer, placed into appropriate EPA- approved containers, labeled, logged onto chain-of-custody documents, and transported on ice to a California state-certified laboratory Copies of the field notes have been included in Attachment A GROUNDWATER SAMPLE ANALYSES AND RESULTS The groundwater samples collected from MWA through MW-7, MWAA, MW-4A, and MW-5A were analyzed for the presence of TPHg, BTEX, and fuel oxygenates MtBE, tert-butyl alcohol (TBA), diisopropyl ether (DIPS), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) using EPA Method 8260B The certified laboratory analytical report and chain-of-custody documentation are ;g presented as Attachment B Groundwater analytical results are presented on Figure 3 and are summarized in Tables 1 and 2 >� Chemical concentrations were generally consistent with historical data Benzene, TPHg, MtBE, and TBA were reported at their lowest concentrations in MWA since sampling was initiated in 1998 INTERIM REMEDIATION The current interim remediation process includes SVE on the horizontal vent wells, in combination with oxygen sparging into SP-1 and SP-1A During the second quarter 2003, mobile SVE was not F; performed at the site due to a pending Permit to Operate through the Jan Joaquin Valley Air Pollution Control District and upgrades to the remediation equipment Mobile SVE will resume once the Permit to Operate is obtained 4, • On April 10, April 21, May 2, and May 12, 2003, SECOR field personnel performed oxygen injection into site sparge wells SP-1 and SP-1A Approximately 150 cubic feet of oxygen was injected into each well simultaneously over a period of approximately 0 8 to 1 5 hours (Table 4) Dissolved 19976 03-2Q Report doc SECOR Intemational Incorporated